The present invention relates to improved self-extinguishing silicone rubber compositions.
While silicone elastomers have many excellent properties, they have the disadvantage of being flammable, and consequently many different methods have been proposed for making the materials self-extinguishing. For example, a typical one of these methods is disclosed in U.S. Pat. No. 3,514,424 in which a platinum-containing material is added to a silicone rubber compound. However, since the self-extinguishing properties caused by the addition of a platinum-containing material are not satisfactory, a large amount of research has been carried out with the intention of improving the self-extinguishing properties by using another compound in combination with the platinum-containing material. Various compounds which are to be added, in combination with platinum-containing materials, to silicone rubber compounds, have been proposed. For example, U.S. Pat. No. 3,652,488 discloses carbon black essentially free of sulfur, U.S. Pat. No. 3,635,874 discloses fumed titanium dioxide, U.S. Pat. No. 3,936,476 discloses finely powdered manganese carbonate, and Japanese Laid-Open Patent Publication No. 50-97644 discloses (FeO).sub.x (Fe.sub.2 O.sub.3).sub.y (where the ratio between x and y is in the range 0.05 to 1.0).
However, these proposed compounds have been unable to provide satisfactory self-extinguishing properties. The silicone rubber compound including the platinum-containing material and carbon black essentially free of sulfur is disadvantageous in that when an organic peroxide containing an acyl group is used as a vulcanizing agent, incomplete vulcanization is caused, thus deteriorating the electric properties of the resulting product. In the case of the silicone elastomer produced by adding both a platinum compound and fumed titanium dioxide, the electric properties will be deteriorated by humidity. In the case of the silicone rubber composition containing a platinum compound and manganese carbonate, incomplete vulcanization will be caused if an organic peroxide containing an acyl group is used as a vulcanizing agent. The product obtained by adding a platinum compound and (FeO).sub.x (Fe.sub.2 O.sub.3).sub.y is disadvantageous in that if the amount of (FeO).sub.x (Fe.sub.2 O.sub.3).sub.y is not large, the resulting self-extinguishing properties will be unsatisfactory, whereas if the amount of (FeO).sub.x (Fe.sub.2 O.sub.3).sub.y is increased, the mechanical properties of the resulting product silicone elastomer will be deteriorated.